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Within BS7671 there is a lot of information in the use of RCBOs and was wondering if in certain applications like industrial sockets BS90437 and lighting Circuits whether these would pose a nuisance tripping action.Just wondering what the general consensus

Ian Stokes

When using high current needs equipment like machinery (ie Milling Machinery and Lathes) would the use of RCBOs pose an inderence with constant tripping as with lighting applications could even leave you without lighting. Just wondering the general consensus? 

  • 0 in reply to Ian Stokes
    Ian Stokes said:
    we need to follow BS7671 which states the use of RCBOs through out

    Not quite.

    Lighting final circuits need additional protection by RCDs in domestic premises (411.3.4).

    Socket outlets not exceeding 32 A also need it, although there are certain exceptions. > 32 A seems unlikely - for 3-phase that would be a 30 bhp motor, so a rather large lathe.

  • 0 in reply to Chris Pearson

    That's for using RCDs socket not exceeding 32A and lighting Circuits and not RCBOs.Is that correct?.

  • 0 in reply to Ian Stokes

    If the sockets do not exceed 32 A (per phase), they need RCD protection. That could be an RCBO in the board, but it could alternatively be a socket-outlet with a built-in RCD.

    MCBs are fine for lighting circuits in commercial premises.

    Clear?

  • 0 in reply to Chris Pearson

    Yeah that's my impression as to some of the sockets coming off these distribution board's are stating 30mA RCD so was thinking that the sockets had the RCD built in them.There are some pictures showing the old board and a RCD at the side of the board so assumed this was related to the board itself and not the sockets.

  • 0 in reply to Ian Stokes
    Ian Stokes said:
    There are some pictures showing the old board and a RCD at the side of the board

    Let's have a look then. (Just drag and drop into the text box.)

  • 0 in reply to Chris Pearson

    BS7671 which states the use of RCBOs through out

    Oh no it doesn't! (a common urban myth amongst some domestic electricians perhaps, but not at all what BS 7671 says). Other than for some special locations (bathrooms, saunas, swimming pools and so on) there are only a few situations where BS 7671 demands 30mA RCD protection, roughly:

    • For sockets (Rated ≤32A - and there are allowable exceptions in some circumstances)
    • For small (≤32A) portable equipment used outdoors (whether though a socket or not)
    • In domestic (household) installations only, for lighting circuits
    • For soft sheathed cables (e.g. T&E) when concealed in a wall (unless given specified significant alternative protection or >50mm deep in a non-conductive wall structure) - that's what mostly drives the domestic requirement for non- lighting/socket circuits. In industrial settings where cabling tends to be surface mounted (or in SWA or in steel conduit) it's a non-issue.

    RCBOs themselves barely get a mention - they're just a convenience where an RCD and MCB functions are wanted together. Using an RCCB (plus a device for overcurrent protection) meets the same requirements - and is quite common even in domestics (think split boards) but obviously with a little more inconvenience if the RCCB is shared across several circuits.

    Also for TT installations you may well need RCDs to provide ADS - and RCBOs might again be convenient for that (but not necessarily 30mA ones unless specifically required for reasons such as those above).

       - Andy.

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